Thalassemia is an autosomal recessive inherited human genetic disorder of the red blood cells (1). It reduces the amount of hemoglobin in a human body, leading to anemia (2). The alpha thalassemia results in a reduced rate of synthesis of alpha globin chain which is the main component of hemoglobin. Alpha thalassemia can be classified into four types and severity of each typed is different depending on the number of the deletion of genetic loci for alpha globin. Alpha thalassemia is commonly found in Southeast Asia, Southern China, India, the Middle East and in the Mediterranean region (3). Due to global migration patterns, there has been an increase in the incidence of thalassemia in many parts of the world (4). There are two major alpha thalassemia carriers, alpha thalassemia1 (alpha0 thalassemia) and alpha thalassemia2 (alpha+thalassemia) carriers. The two alpha globin genes on the same chromosome are deleted in alpha thalassemia1. There is only one alpha globin gene deletion in an alpha thalassemia2. Moreover, some abnormal hemoglobin such as Hb Constant Spring (Hb CS) and Hb Pakse also affect the alpha globin gene expression and behave like and alpha thalassemia2. The interaction between these abnormal genes lead to many alpha thalassemia syndromes such as homozygous alpha thalassemia, Hb H disease (alpha thalassemia1/and alpha thalassemia2 or alpha thalassemia1/Hb CS) and Hb Bart's hydrops fetalis (homozygous alpha thalassemia1). Heterozygote screening and genetic counseling are essential for the prevention and control of severe thalassemia diseases (5).
Small amount of Hb Bart's is presented in the blood of some alpha thalassemia carriers. The immunochromatographic strip test can detect Hb Bart's in alpha thalassemia1 carrier and all other alpha thalassemia syndromes carry this abnormal gene such as Hb H disease, AE Bart's disease and Hb Bart's hydrops fetalis. The test is also positive in homozygote for alpha thalassemia2. Thus this test will help to prevent severe alpha thalassemia disorders in many populations.
The immunochromatographic strip is a qualitative, lateral flow immunoassay for the screening of various types of alpha thalassemia trait by using whole blood. As the blood test sample (hemolysate) diffuses through the absorbent test strip, the labeled antibody-colloidal gold conjugate binds to the Hb Bart's in the specimen forming an antibody-antigen complex. This complex binds to the anti Hb Bart's antibody in the test line and expresses a purple-red band. The absence of a colored band in the test region indicates a negative result. The reaction mixture continues flowing through the absorbent device past the test and control lines. Unbound conjugate binds to the reagents in the control line, producing a pink color band, demonstrating that the reagents and test strip are functioning correctly.